The present invention relates to a process for the manufacture of soft polyvinyl chloride foams from foamable plastisols.
Gelling and foaming of polyvinyl chloride pastes is achieved by heating the paste, but this heating process can be difficult and complicated. These difficulties arise primarily due to the good insulation properties of polyvinyl chloride and especially, of polyvinyl chloride foams, which make it difficult to heat the inner parts of a large mass of polyvinyl chloride without overheating the outer parts.
One conventional method that is used for the manufacture of polyvinyl chloride foam is to heat the foamable paste in a gelatination channel. Apart from being both expensive and spaceconsuming, this method has the disadvantage that only relatively thin foam sheets can be produced because of the heating difficulties mentioned above. In any case, very long gelatination channels would be necessary for thicker sheets. Blocks of foam have had to be manufactured by more expensive methods using high frequency heating. A further method of foaming is by the use of a rotary mould for the production of foam articles. This method is again complex, and heating difficulties occur with larger shapes and articles.